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A103008
Numbers n such that 5*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
2, 9, 12, 15, 26, 45, 62, 80, 128, 326, 494, 614, 710, 1641, 1646, 2103, 8514, 8688
OFFSET
1,1
COMMENTS
Also numbers n such that (47*10^n-11)/9 is prime.
No other terms below 50000.
a(19) > 10^5. - Robert Price, Jul 04 2015
FORMULA
a(n) = A101573(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(47*10^n - 11)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A207967 A265413 A297830 * A124742 A152003 A251428
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 18 2005
STATUS
approved